Wow, never really thought about the inappropriate age thing, particularly at 14 months.... DD is 4 yo and she still showers with DH or I and occassionally baths with us. She did go through a stage when younger where she's point at DH privates, but she is sort of over that now.
I know a lady whos DH refused to shower with his girls unless he had his bathers on, even when they were young - each to their own.
I agree though, when DD has said enough is enough, then I guess for us that will be time to stop sharing baths & showers.